1. Field of the Invention
The present invention relates to a recording apparatus including a magnetic linear encoder for detecting a position and a velocity of a carriage mounted with a recording head.
2. Related Background Art
A generally known practice in the conventional recording apparatus is that detecting a position and a velocity of a carriage mounted with a recording head involves the use of an optical linear encoder and a magnetic linear encoder.
The optical linear encoder includes a scale element composed of a slit-like film on the side of an apparatus body. The carriage moving relatively to this scale element is mounted with a reading unit consisting of a transmissive or reflective sensor. This optical encoder is simple but fragile against dust. Further, high-density slits are limited in terms of a working accuracy in working based on an etching system or a laser working system. This leads to remarkably high costs for obtaining the high working accuracy.
Contrastingly, the magnetic linear encoder is capable of reading in a non-contact manner and more resistive against dust than the optical linear encoder. In addition, a magnetization density can be increased more easily in the magnetic linear encoder than in the optical one.
One of the points to which attention is particularly paid when using the magnetic linear encoder is a gap between an MR device (ferromagnetic substance magneto-resistance effect device) and the scale element. The magnetic encoder is constructed such that both ends of the scale element magnetized are fixed to the apparatus body, and the detection unit consisting of the MR device is fixed onto the carriage moving relatively to this scale element by use of a screw or the like. FIG. 27 illustrates how the scale element of the magnetic linear encoder is attached to the recording apparatus body. Referring to FIG. 27, a recording head (hereinafter simply termed a head) 101 is fixed to a carriage 102. This carriage 102 is supported and guided by guide shafts 104, 105. The carriage 102 is driven in arrowed directions A, B by means of a driving motor (unillustrated) through a timing belt (not shown). Recording is effected by the recording head 101 on a recording medium 106. The guide shafts 104, 105 are fixed to side plates 103a, 103b of the recording apparatus body. The head 107 of the magnetic linear encoder is fixedly positioned with respect to the carriage 102. Both ends of a scale element 108 of the magnetic linear encoder are fixedly positioned to the side plates 103a, 103b by support members 108a, 108b.
Further, according to another example of the method of attaching the scale element of the magnetic linear encoder to the recording apparatus body, as illustrated in FIG. 28, one end of the scale element is fixed, while the other end thereof is provided with a spring 207 for giving a tension to the scale element 4.
In the conventional examples, however, the detection unit of the magnetic linear encoder is fixed to the carriage with the screw or the like. Tools such as a driver, etc. are therefore required. Besides, the scale element of the magnetic linear encoder has a weak point that the magnetized information is damaged due to a contact with a substance bearing magnetism. As explained earlier, when using the driver for fixing the detection unit, the driver mistakenly comes into contact with the scale element, resulting in such a problem that the magnetized information of the scale element is disordered.
Further, the recording apparatus, when employing sheets having different thicknesses, may take the following methods. The recording head mounted on the carriage and the surface of the sheet are kept at a fixed distance. For this purpose, the carriage is rotated about a carriage shaft. The carriage shaft is moved back and forth with respect to the sheet. In this case, the detection unit is fixed to the carriage and therefore moves with a movement of the carriage. Both ends of the scale element are, however, fixed to the recording apparatus body, and, therefore, the scale element does not move with the movement of the carriage. Accordingly, both ends of the scale element and the detection unit on the carriage are not aligned. As a result, an extra load is exerted on the movement of the carriage in the scan direction. Additionally, there arises a problem in which this causes a deformation of the scale element and abrasion of the bearings at both edges of the detection unit.
Moreover, the detection unit is constructed of the MR device, a holding portion for this MR device and oil-impregnated bearings press-fitted in both edges of this holding portion. A gap, i.e., the most important element to this magnetic linear encoder, between the MR device and the scale element is determined by the above components. However, an accuracy on the order of several 10 microns is demanded. Consequently, there exists a problem in which the accuracy is harder to obtain with a larger number of components.
Further, the conventional method of attaching the scale element of the magnetic linear encoder to the recording apparatus body presents such a problem that the sliding load of the carriage increases in a position close to the side plate in the following cases. The scale element of the magnetic linear encoder is attached in non-parallel to the guide shaft. There deviate the fitting positions of the support members for the scale element of the magnetic linear encoder and of the head. This will hereinafter be described in detail with reference to FIGS. 29 to 31.
FIG. 29 is a schematic plan view showing a state where the scale element of the magnetic linear encoder is attached in non-parallel to the guide shaft. FIG. 30 is a schematic plan view showing a state where there deviate the mounting positions of the scale element of the magnetic linear encoder and of the head.
Referring to FIG. 29, the guide shaft 104 is not in parallel to the scale element 8 of the magnetic linear encoder. The carriage 102 is guided by the guide shaft 104 and moved to an area a or b in the vicinity of a side plate 103a or 103b. At this time, the head 107 is fixed to the carriage 102. Therefore, it follows that the scale element 108 undergoes flexures of approximately 1.sub.1, 1.sub.2 in the respective areas. FIG. 31 shows a sliding load characteristic of the carriage with respect to a carriage position. As illustrated in FIG. 31, the sliding load of the carriage with respect to the carriage position becomes approximately L.sub.a, L.sub.b in the vicinities of the side plates 103a, 103b. It follows that an increase in the sliding load is considerably greater than a load L.sub.0 when the carriage is located in the vicinity of the center.
Further, similarly in the case where there deviate the mounting positions of the scale element of the magnetic linear encoder and of the head, the carriage 102 is guided by the guide shaft 104 and moved to the areas a, b in the vicinities of the side plates 103a, 103b. At this time, the head is fixed to the carriage 102. Hence, it follows that the scale element 108 undergoes a flexure of approximately 1.sub.1 in the respective areas. Similarly in the above-mentioned case, as shown in FIG. 31 of the sliding load characteristic of the carriage with respect to the carriage position, the sliding load of the carriage with respect to the carriage position becomes about L.sub.a in the vicinities of the side plates 103a, 103b. It follows that the sliding load increases well above the load L.sub.0 when the carriage is located in close proximity to the center.
The above fluctuations in the sliding load of the carriage conduce to vibrations when the carriage makes a motion at a constant speed. Further, serious problems arise, wherein noises are produced when the carriage moves, and a printing quality declines.
Furthermore, the sliding load between the scale element of the magnetic linear encoder and the head fluctuates (and simultaneously augments). Consequently, the following serious problems are also caused. The bearings of the head are abraded, and an air gap between the MR device and the magnetized portion is narrowed enough to break down the MR device or reversely widened enough to worsen a reading condition.
Moreover, another conventional method of attaching the scale element of the magnetic linear encoder to the recording apparatus body has defects which follow. A large number of parts involves a laborious assembly. Needed also is an operation to keep the parallelism with the shaft for guide-moving the carriage in the scan direction. This is a factor for an increase in costs.